System and method for updating a sleep ID of a mobile station in a BWA communication system

ABSTRACT

A system and method for updating a sleep identifier (SLPID) of a mobile station (MS) in a broadband wireless access (BWA) communication system having a sleep mode in which there is no transmission data and an awake mode in which there is transmission data. Upon recognizing a need to update an SLPID allocated to an MS in the sleep mode in the initial phase of the sleep mode, a base station (BS) reallocates a new SLPID to be allocated to the MS and transmits SLPID update information to the MS. Upon receiving the SLPID update information for its current SLPID during the sleep mode, the MS updates its current SLPID with the reallocated SLPID according to the received update information.

PRIORITY

This application is a continuation of U.S. patent application Ser. No.11/205,597 filed Aug. 17, 2005, and claims the benefit under 35 U.S.C.§119(a) of an application entitled “System and Method for Updating SleepID of Mobile Station in a BWA Communication System” filed in the KoreanIntellectual Property Office on Aug. 17, 2004 and assigned Serial No.2004-66576, the entire contents of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a Broadband Wireless Access(BWA) communication system, and in particular, to a method for updatinginformation on a sleep identifier allocated to a mobile station, and asystem using the same.

2. Description of the Related Art

Active research on the 4^(th) generation (4G) communication system,which is the next generation communication system, is being conducted toprovide users with high-rate services supporting variousQuality-of-Services (QoSs). Recently, many studies of the 4 Gcommunication system are being made to support a high-speed servicecapable of guaranteeing the mobility and the QoS in a BWA communicationsystem such as a wireless Local Area Network (LAN) system and a wirelessMetropolitan Area Network (MAN) system. The typical example BWA systemis the Institute of Electrical and Electronics Engineers (IEEE) 802.16acommunication system or the IEEE 802.16e communication system.

The IEEE 802.16a communication system and the IEEE 802.16e communicationsystem utilize Orthogonal Frequency Division Multiplexing (OFDM) andOrthogonal Frequency Division Multiple Access (OFDMA) to support abroadband transmission network for a physical channel of the wirelessMAN system. More specifically, the IEEE 802.16a communication systemdoes not consider the mobility of subscriber stations (SSs), i.e., isdirected to fixed MSs and a unicell structure. However, the IEEE 802.16ecommunication system considers the mobility of the SSs. Herein, an SShaving the mobility will be referred to as a mobile station (MS).

The IEEE 802.16e communication system, as it considers the mobility ofMSs, has a problem of high MS power consumption compared with othersystems. As a typical method for minimizing the MS power consumption, asleep mode and an awake mode between the MS and a base station (BS) havebeen proposed. In this case, the MS performs a ranging operation ofperiodically adjusting a timing offset, a frequency offset, and powerwith the BS in order to cope with a change in the quality of a channelto the BS. In particular, a periodic ranging operation is very importantfor the IEEE 802.16e communication system as it considers the mobilityof MSs.

FIG. 1 is a diagram illustrating a sleep mode operation of aconventional IEEE 802.16e communication system. However, before adescription of FIG. 1 is given, it should be noted that the sleep modehas been proposed to minimize MS power consumption in an idle intervalfor which no packet data is transmitted, during transmission of packetdata. That is, in the sleep mode, an MS and a BS simultaneouslytransition to the sleep mode to minimize the MS power consumption in theidle interval in which no packet data is transmitted.

Generally, the interval for which no packet data is transmitted is equalin operation to the interval for which packet data is transmitted.Because such an operation is unreasonable, the sleep mode has beenproposed. If there is packet data to transmit in the sleep mode, boththe BS and the MS must simultaneously transition to the awake mode totransmit and receive packet data.

The sleep mode has been proposed to minimize the power consumption andinter-channel interference. However, because packet data is affected bytraffic, the traffic characteristic and transmission type characteristicmust be taken into consideration in the sleep mode operation.

Referring to FIG. 1, reference numeral 110 denotes a packet datageneration format. The packet data generation format 110 includes aplurality of ON intervals and a plurality of OFF intervals. The ONintervals are burst intervals for which packet data, i.e., traffic, isgenerated, and the OFF intervals are idle intervals for which no trafficis generated. According to the traffic generation pattern, the MS andthe BS alternately transition (mode change) to the sleep mode and theawake mode, thereby minimizing power consumption of the MS and cancelinginterference between channel signals.

Reference numeral 120 denotes a mode change format for the MS and theBS. The mode change format 120 for the MS and the BS includes aplurality of awake modes and a plurality of sleep modes. The awake modesrepresent the modes in which traffic is generated, and in the awakemodes, actual transmission and reception of packet data is achieved. Thesleep modes represent the modes in which no traffic is generated, and inthe sleep modes, actual transmission and reception of the packet data isnot achieved.

Reference numeral 130 denotes an MS power level format that represents apower level of the MS according to the packet data generation format 110and the mode change format 120. In the MS power level format 130, an MSpower level for the awake mode is represented by ‘K’, and an MS powerlevel for the sleep mode is represented by ‘M’. Comparing the MS powerlevel K for the awake mode with the MS power level M for the sleep mode,the M is much less than the K. That is, in the sleep mode, because thereis no packet data transmission/reception, the power consumption isinsignificant.

A description will now be made herein below of the schemes currentlyproposed to support the sleep mode operation in the IEEE 802.16ecommunication system. However, before a description of the schemescurrently proposed in the IEEE 802.16e communication system is given,the following preconditions will be described.

In order to transition to the sleep mode, the MS must receive a modechange approval from the BS. The BS transmits an approval for transitionto the sleep mode to the MS and then transmits packet data. The BS musttransmit information indicating the presence of transmission packet datato the MS, during a listening interval of the MS. In this case, the MSmust awake from the sleep mode and determine if there is packet data tobe transmitted thereto from the BS.

If it is determined that there is packet data to be transmitted theretofrom the BS, the MS transitions to the awake mode and receives packetdata form the BS. However, if it is determined that there is no packetdata to be transmitted thereto from the BS, the MS can either return tothe sleep mode or maintain the awake mode.

Parameters for Supporting Sleep Mode and Awake Mode Operations

A description will now be made of the parameters required to support thesleep mode and awake mode operations currently proposed in the IEEE802.16e communication system.

(1) Sleep Identifier (SLPID)

The SLPID is a value that an MS is allocated through a Sleep-Response(SLP-RSP) message for transitioning from the awake mode to the sleepmode, and is uniquely allocated only to the MSs in the sleep mode. Thatis, the SLPID is an ID used for identifying an MS in the sleep modeincluding the listening interval, and if the corresponding MS makes amode change from the sleep mode to the awake mode, the SLPID previouslyallocated to the MS is returned to the BS so that another MS wanting totransition to the sleep mode can reuse the SLPID through the SLP-RSPmessage. Commonly, the SLPID has a 10-bit size, and thus can be used foridentifying a total of 1024 MSs in sleep mode operation.

(2) Sleep Interval

The sleep interval is an interval that a BS allocates to an MS at therequest of the MS, and represents the time interval for which the MSmaintains the sleep mode until a listening interval starts after the MSmakes a mode change from the awake mode to the sleep mode. That is, thesleep interval is defined as the total time interval for which the MS isin the sleep mode.

The MS can continuously maintain the sleep mode if there is no datatransmitted from the BS even after the sleep interval. In this case, theMS updates the sleep interval while increasing the sleep interval usingpredetermined initial-sleep window and final-sleep window values. Theinitial-sleep window value represents an initial minimum value of thesleep interval, and the final-sleep window value represents a finalmaximum value of the sleep interval. The initial-sleep window value andthe final-sleep window value can be represented by the number of frames.

The listening interval is an interval that a BS allocates to an MS atthe request of the MS. The listening interval corresponds to the timeinterval for which the MS temporarily awakes to receive downlinkmessages such as a traffic indication (TRF-IND) message from the BSduring the sleep mode operation, and in the listening interval, the MScan receive the downlink messages in synchronism with a downlink signalfrom the BS. The TRF-IND message indicates if there is traffic to betransmitted to the MS, i.e., indicates if there is packet data.

The MS continuously waits for the reception of the TRF-IND message forthe listening interval. If a bit indicating the MS in an SLPID bitmapincluded in the TRF-IND message represents a positive indication value,the MS continuously maintains the awake mode, thereby transitioning tothe awake mode. However, if the bit indicating the MS in the SLPIDbitmap included in the TRF-IND message represents a negative indicationvalue, the MS transitions back to the sleep mode.

(3) Sleep Interval Update Algorithm

Upon transitioning to the sleep mode, the MS determines a sleepinterval, regarding the minimum window value as the minimum sleep modeinterval. Thereafter, if the MS wakes up from the sleep mode for thelistening interval and determines that there is no packet data to betransmitted from the BS, the MS sets the sleep interval to an intervalthat is 2 times the previous sleep interval, and continuously maintainsthe sleep mode. For example, if the minimum window value is ‘2’, the MSsets the sleep interval to an interval of 2 frames, and then maintainsthe sleep mode for the 2 frames. After a lapse of the 2 frames, the MSawakes from the sleep mode for the listening interval, and determines ifa TRF-IND message is received. If the TRF-IND message is not received,i.e., if there is no packet data to be transmitted thereto from the BS,the MS sets the sleep interval to a 4-frame interval, which is 2 timesthe 2-frame interval, and then maintains the sleep mode for the 4frames. Accordingly, the sleep interval can increase between the minimumwindow value and the maximum window value.

Messages for Supporting Sleep Mode and Awake Mode Operation

A description will now be made of the messages currently defined tosupport the sleep mode and awake mode operations in the IEEE 802.16ecommunication system.

(1) Sleep-Request (SLP-REQ) Message

The SLP-REQ message, a message transmitted from an MS to a BS, is usedwhen the MS requests a mode change to the sleep mode. The SLP-REQmessage includes the parameters, or information elements (IEs), requiredby the MS to operate in the sleep mode. A format of the SLP-REQ messageis shown below in Table 1.

TABLE 1 Syntax Size Notes SLP-REQ_Message_Format( ) { Management messagetype = 50 8 bits Initial-sleep window 6 bits Final-sleep window 10 bits Listening interval 6 bits Reserved 2 bits }

The SLP-REQ message is a dedicated message transmitted on the basis of aconnection ID (CID) of an MS, and IEs of the SLP-REQ message include aManagement Message Type, an Initial-Sleep Window, a Final-Sleep Window,and a Listening Interval. The Management Message Type indicates a typeof the current transmission message, and Management Message Type=50indicates the SLP-REQ message. The Initial-Sleep Window indicates arequested start value for the sleep interval (measured in frames), andthe Final-Sleep Window indicates a requested stop value for the sleepinterval (measured in frames). That is, as described with reference tothe sleep interval update algorithm, the sleep interval can be updatedbetween the initial-window value and the final-window value. TheListening Interval indicates a requested listening interval (measured inframes), and the listening interval can also be represented by thenumber of frames.

(2) Sleep-Response (SLP-RSP) Message

The SLP-RSP message, a response message to the SLP-REQ message, can beused to approve or deny a mode change to the sleep mode requested by theMS, or can be used to indicate an unsolicited instruction. The SLP-RSPmessage includes IEs needed by the MS to operate in the sleep mode, anda format of the SLP-RSP message is shown in Table 2.

TABLE 2 Syntax Size Notes  MOB-SLP-RSP_Message_Format( ) { Managementmessage type = 51  8 bits Sleep-approved  1 bit 0: Sleep-mode requestdenied 1: Sleep-mode request approved If (Sleep-approved == 0) {  1 bit0: The MS may retransmit the MOB_SLPREQ message after the time duration(REQ-duration) given by the BS in this message 1: The MS shall notretransmit the MOB_SLPREQ message and shall await the MOB_SLPRSP messagefrom the BS REQ-duration  4 bits Time duration for case whereAfter-REQ-action value is 0 reserved  2 bits  }  else {   Start frame  initial-sleep windows  6 bits   final-sleep windows 10 bits  listening interval  6 bits   SLPID 10 bits  } }

The SLP-RSP message is also a dedicated message transmitted on the basisof a Basic CID of an MS, and IEs of the SLP-RSP message illustrated inTable 2 will be described below.

Management Message Type indicates a type of the current transmissionmessage, and Management Message Type=51 indicates the SLP-RSP message.Sleep-Approved is expressed with 1 bit, wherein Sleep-Approved=0indicates sleep-mode request denied and Sleep-Approved=1 indicatessleep-mode request approved. More specifically, Sleep-Approved=0indicates that a mode change to the sleep mode requested by the MS isdenied by the BS. Upon receiving the denial, the MS transmits theSLP-REQ message to the BS according to conditions, or waits for thereception of the SLP-RSP message indicating unsolicited instruction fromthe BS.

For Sleep-Approved=1, the SLP-RSP message includes Start Frame,Initial-Sleep Window, Final-Sleep Window, Listening Interval, and SLPID.For Sleep-Approved=0, the SLP-RSP message includes After-REQ-Action andREQ-Duration. The Start Frame value indicates a frame value up to thetime when the MS enters the first sleep interval, and does not includethe frame where the SLP-RSP message is received (the number of frames(not including the frame in which the message has been received) untilthe MS shall enter the first sleep interval). That is, the MStransitions to the sleep mode after a lapse of frames corresponding tothe start frame value from the next frame after the frame over which theSLP-RSP message has been received. The SLPID is used for identifying MSsin the sleep mode, and can be used for identifying a total of 1024 MSsin the sleep mode.

As described above, the Initial-Sleep Window value indicates a startvalue for the sleep interval (measured in frames), and the listeninginterval value indicates a value for the listening interval (measured inframes). The Final-Sleep Window value indicates a stop value for thesleep interval (measured in frames). The After-REQ-action valueindicates an operation that the MS, whose request to the sleep mode hasbeen denied, must perform.

(3) Traffic Indication (TRF-IND) Message

The TRF-IND message, a message transmitted from a BS to an MS for thelistening interval, indicates the presence of packet data to betransmitted from the BS to the MS. A format of the TRF-IND message isshown below in Table 3.

TABLE 3 Syntax Size Notes  MOB-TRF-IND_Message_Format( ){ ManagementMessage Type = 52  8 bits FMT  1 bit 0 = SLPID based format 1 = CIDbased format if(FMT==0){  Byte of SLPID bitmap  8 bits  SLPID bitmapVariable } else {  Num-pos  7 bits Number of CIDs on the positiveindication list  for(i=0 ; i<Num-pos ; i++){   Short Basic CID 12 bitBasic CID  }  while (!byte_boundary){   Padding bits 1 padding for bytealignment  } } }

The TRF-IND message is a broadcasting message that is transmitted on abroadcasting basis, unlike the SLP-REQ message and the SLP-RSP message.The TRF-IND message indicates the presence/absence of packet data to betransmitted from the BS to a particular MS, and the MS encodes thebroadcasted TRF-IND message for the listening interval, and determineswhether to transition to the awake mode, or to transition back to thesleep mode, according to the decoding result.

When determining to transition to the awake mode, the MS detects framesynchronization, and if a corresponding frame sequence number is notidentical to a frame sequence number expected by the MS, the MS canrequest retransmission of the packet data lost in the awake mode.Otherwise, if the MS fails to receive the TRF-IND message for thelistening interval, or if a value indicating positive indication is notincluded in the TRF-IND message even though the TRF-IND message isreceived, the MS may return to the sleep mode.

For the IEs in the TRF-IND message, Management Message Type indicates atype of the current transmission message, and Management Message Type=52indicates the TRF-IND message. FMT indicates whether to use an SLPID ora Basic CID of an MS in the process of indicating the presence/absenceof the traffic to be transmitted to the MS in the sleep mode. When theSLPID is used for the indication, the SLPID bitmap indicates a set ofindication indexes allocated bit by bit to each of the SLPIDs allocatedto MSs to identify the MSs that has transitioned to the sleep mode. Thatis, the SLPID bitmap indicates a group of bits allocated bit by bit toeach MS, for (maximum value-1) SLPIDs among the SLPIDs allocated to theMS in the sleep mode. The SLPID bitmap may be allocated dummy bitsthrough byte alignment.

One bit allocated to the MS indicates the presence/absence of data to betransmitted from the BS to the corresponding MS. Therefore, an MS in thesleep mode reads a bit mapped to an SLPID that was allocated during amode change to the sleep mode from the TRF-IND message received for thelistening interval, and if the read bit indicates a positive indicationvalue, i.e., a value of ‘1’, the MS continuously maintains the awakemode, thereby transitioning to the awake mode. Otherwise, if theallocated bit indicates a negative value, i.e., a value of ‘0’, the MStransitions back to the sleep mode.

The BS sequentially allocates SLPIDs to MSs entering the sleep mode inthe order of an SLPID with the smaller number among unallocated SLPIDs.During the sleep mode, the MS continuously uses the fixed SLPIDallocated from the BS in the initial phase of the sleep mode until itreturns to the awake mode.

In this case, each MS that has entered the sleep mode must read theSLPID bitmap from its beginning until a corresponding part where its ownSLPID is located, in order to determine the present/absence of packetdata transmitted thereto. Because the SLPID that the MS is allocated isfixed to the initially allocated number, if there are many unallocatedempty SLPIDs in the SLPID bitmap, there is a considerable waste ofresources and time required for reading SLPIDs. That is, increasing thenumber of MSs entering the sleep mode increases SLPID numbers allocatedto the MSs. Therefore, an MS with a greater SLPID number, as itsallocated SLPID number is fixed, has a long processing time for readingand processing the SLPID bitmap up to its traffic SLPID. In addition,though the number of MSs that have actually entered the sleep mode isnot large, if a difference between the least SLPID and the greatestSLPID among the SLPIDs allocated to the MSs is great, the SLPID bitmapexcessively increases.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been designed to solve the aboveand other problems occurring in the prior art.

It is, therefore, an object of the present invention to provide a methodfor updating a sleep identifier (SLPID) allocated to a mobile station(MS) in a sleep mode in a Broadband Wireless Access (BWA) communicationsystem, and a system using the same.

It is another object of the present invention to provide a method andsystem for reducing a processing time for reading and processing anSLPID by an MS through SLPID updating, such that the SLPID bitmap is notunnecessarily increased and effectively managed.

It is further another object of the present invention to provide amethod and system for periodically updating and managing, by an MS, anSLPID allocated from a base station (BS) during transition to a sleepmode in a BWA communication system.

According to one aspect of the present invention, there is provided amethod for updating a sleep identifier (SLPID) of a mobile station (MS)in a broadband wireless access (BWA) communication system having a sleepmode in which there is no transmission data and an awake mode in whichthere is transmission data, the sleep mode having a sleep interval forwhich data reception is impossible and a listening interval for whichdata reception is possible. The method includes the steps of:recognizing a need to update an SLPID allocated to an MS in the sleepmode in the initial phase of the sleep mode; reallocating, by a basestation (BS), a new SLPID to be allocated to the MS; transmitting theSLPID to the MS; receiving update information for its current SLPIDduring the sleep mode; and updating, by the MS, its current SLPID withthe reallocated SLPID according to the received update information.

According to another aspect of the present invention, there is provideda method for updating, by a base station (BS), a sleep identifier(SLPID) allocated to a mobile station (MS) in a broadband wirelessaccess (BWA) communication system having a sleep mode in which there isno transmission data and an awake mode in which there is transmissiondata, the sleep mode having a listening interval for which datareception is possible. The method includes the steps of: determining ifthere is a need to update an SLPID of an MS in the sleep mode;determining an SLPID allocable to the MS if there is a need to updatethe SLPID of the MS; creating SLPID update information including thedetermined SLPID if an SLPID to be newly allocated to the MS isdetermined; and transmitting the SLPID update information to the MS.

According to further another aspect of the present invention, there isprovided a method for updating a sleep identifier (SLPID) by a mobilestation (MS) in a broadband wireless access (BWA) communication systemhaving a sleep mode in which there is no transmission data and an awakemode in which there is transmission data, the sleep mode having a sleepinterval for which data reception is impossible and a listening intervalfor which data reception is possible. The method includes the steps of:receiving a predetermined indication message including an SLPID updateindicator; checking SLPID update information included in the receivedindication message; and if an SLPID update indicator and a new SLPID areallocated in the update information, updating a current SLPID with thenew SLPID.

According to yet another aspect of the present invention, there isprovided a system for updating a sleep identifier (SLPID) of a mobilestation (MS) in a broadband wireless access (BWA) communication systemhaving a sleep mode in which there is no transmission data and an awakemode in which there is transmission data, the sleep mode having a sleepinterval for which data reception is impossible and a listening intervalfor which data reception is possible. The system includes: an MS; and abase station (BS) for, upon recognizing a need to update an SLPIDallocated to the MS in the sleep mode in the initial phase of the sleepmode, reallocating a new SLPID to be allocated to a corresponding MS andtransmitting the SLPID to the corresponding MS. The MS, upon receivingSLPID update information from the BS during the sleep mode, updates itscurrent SLPID with the reallocated SLPID according to the receivedupdate information.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features, and advantages of the presentinvention will become more apparent from the following detaileddescription when taken in conjunction with the accompanying drawings inwhich:

FIG. 1 is a diagram illustrating a sleep mode operation of aconventional IEEE 802.16e communication system;

FIG. 2 is a flowchart illustrating an SLPID update process by a BS in acommunication system according to an embodiment of the presentinvention;

FIG. 3 is a flowchart illustrating an SLPID update process by an MS in acommunication system according to an embodiment of the presentinvention;

FIG. 4 is a flowchart illustrating an SLPID update process by a BS usinga TRF-IND message in a communication system according to an embodimentof the present invention;

FIGS. 5A and 5B are flowcharts illustrating an SLPID update process byan MS using a TRF-IND message in a communication system according to anembodiment of the present invention;

FIG. 6 is a flowchart illustrating an SLPID update process by a BS usingan unsolicited SLP-RSP message in a communication system according to anembodiment of the present invention;

FIG. 7 is a flowchart illustrating an SLPID update process by an MSusing an unsolicited SLP-RSP message in a communication system accordingto an embodiment of the present invention;

FIG. 8 is a flowchart illustrating an SLPID update process by a BS usingan unsolicited SLP-RSP message in a communication system according toanother embodiment of the present invention; and

FIG. 9 is a flowchart illustrating an SLPID update process by an MSusing an unsolicited SLP-RSP message in a communication system accordingto another embodiment of the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Several exemplary embodiments of the present invention will now bedescribed in detail with reference to the annexed drawings. In thefollowing description, a detailed description of known functions andconfigurations incorporated herein has been omitted for conciseness.

The present invention proposes a sleep identifier (SLPID) updatingscheme for a mobile station (MS) in a sleep mode in an Institute ofElectrical and Electronics Engineers (IEEE) 802.16e communicationsystem, which is a Broadband Wireless Access (BWA) communication system.“SLPID updating” refers to a process in which a base station (BS)reallocates a new SLPID to an MS in the sleep mode during the sleep modeoperation, instead of the SLPID allocated in the initial phase of thesleep mode process. Accordingly, the present invention can efficientlymanage SLPID resources through the SLPID updating.

Although the present invention, by way of example, will be describedherein with reference to the IEEE 802.16e communication system, thepresent invention can also be applied to all other communication systemssupporting the sleep mode operation and periodic ranging in the sleepmode operation.

First Embodiment

In an SLPID update method according to a first embodiment of the presentinvention, a BS updates an SLPID in a periodic ranging operation with anMS in a sleep mode. However, before a description of a periodicranging-based SLPID update method according to the first embodiment ofthe present invention is given, a brief description will now be made ofthe ranging.

The ranging is classified into initial ranging, periodic ranging, andbandwidth request ranging. Before transmitting data through the rangingoperation, an MS can correct transmission power and correct a timingoffset and a frequency offset.

The initial ranging is ranging performed by a BS to acquiresynchronization with an MS, and the initial ranging is performed todetect a correct timing offset between the MS and the BS and to correcttransmission power. That is, upon power-on, the MS performs the initialranging to acquire synchronization with the BS by receiving a DL-MAPmessage and a UL-MAP message and to correct the timing offset and thetransmission power with the BS.

The periodic ranging represents ranging periodically performed by the MSto correct channel conditions with the BS after correcting the timingoffset and transmission power with the BS through the initial ranging,and the bandwidth request ranging is ranging in which the MS requestsallocation of a bandwidth to perform actual communication with the BSafter correcting the timing offset and transmission power with the BSthrough the initial ranging.

As described above, because the IEEE 802.16e communication systemconsiders the mobility of MSs, the periodic ranging for the MSs is veryimportant for reliable data transmission/reception. The periodic rangingis an operation for measuring and correcting the parameters required forenabling the MS to communicate with a BS. The BS must allocate uplinkresources such that the MS can perform periodic ranging, i.e., the MScan transmit a ranging request (RNG-REQ) message to the BS. That is, theBS must allocate uplink resources to the MS for periodic ranging of theMS, and must transmit the uplink resource allocation information to theMS through a UL-MAP message.

The MS transmits the RNG-REQ message to the BS through the uplinkresource allocated from the BS, thereby performing periodic ranging withthe BS. The BS corrects the transmission power, timing offset, andfrequency offset according to the RNG-REQ message received from the MS,and then transmits a ranging response (RNG-RSP) message to the MS inresponse to the RNG-REQ message, ending the periodic ranging. Even theMS in the sleep mode must perform the periodic ranging to reliablycommunicate with the BS.

FIG. 2 is a flowchart illustrating an SLPID update process performed ina BS in a periodic ranging operation with an MS in a sleep mode in acommunication system according to an embodiment of the presentinvention. Referring to FIG. 2, in step 201, a BS receives an RNG-REQmessage for periodic ranging from an MS in a sleep mode. In step 203,the BS determines if there is a need to update an SLPID of the MS in thesleep mode. More specifically, in step 203, the BS determines if thereis an empty SLPID in a list of SLPIDs with a number less than that ofthe current SLPID of the corresponding MS in the total SLPID listmanaged in the BS. The empty SLPID can correspond to an SLPID returnedto the BS when another MS using the SLPID previously allocated from theBS transitions to the awake mode. If there are a plurality of emptySLPIDs, it is preferable to newly allocate and update the least SLPIDamong the empty SLPIDs. In this manner, an SLPID of the MS can becontinuously updated with a smaller SLPID rather than being fixed to theinitially allocated SLPID.

For example, assuming that the lowest SLPID that the BS can allocate tothe MS in the sleep mode is an SLPID#1 and an SLPID initially allocatedto the MS is an SLPID#99, if there are unused SLPIDs between the SLPID#1and the current SLPID#99 for the MS that has transmitted the RNG-REQmessage, the BS can newly allocate the least one of the empty SLPIDs tothe MS.

If it is determined in step 203 that there is a need to update the SLPIDof the MS, i.e., if the BS determines the presence of unused SLPIDsbetween the least SLPID allocable to the MS in the sleep mode and theSLPID of the MS, the BS creates an RNG-RSP message including informationused for updating the SLPID of the MS in the sleep mode in step 205.That is, the BS creates an SLPID currently used by the MS and SLPIDinformation to be newly allocated to the MS in an SLPID_Update field ofthe RNG-RSP message, which is a response message to the RNG-REQ message,and stores the RNG-RSP message. Preferably, the BS creates the currentSLPID used by the MS and the SLPID information to be newly allocated tothe MS in pair.

Thereafter, in step 207, the BS transmits the RNG-RSP message includingthe created SLPID information to the MS. However, if it is determined instep 203 that there is no need to update the SLPID of the MS, the BStransmits an RNG-RSP message with no SLPID_Update value to the MS instep 207.

The SLPID_Update parameter added to a Type/Length/Value (TLV) Encodingparameter of the RNG-RSP message is shown below in Table 4.

TABLE 4 Name Type Length Value SLPID_Update 18 variable compound NameType (1 byte) Length Value (Variable length) Old_New_SLPID 18.1 20 bitsThe first 10 bits indicate old SLPID and the last 10 bits indicate newSLPID

Referring to Table 4, the SLPID_Update parameter includes Old_New_SLPIDin which an OLD SLPID currently allocated to the MS and a NEW SLPID tobe newly allocated to the MS are stored in pair.

As shown in Table 4, the SLPID_Update parameter, as it is a TLV Encodingtype parameter, is transmitted to the MS through the RNG-RSP messageonly when necessary. That is, the BS transmits the SLPID_Updateparameter to the MS through the RNG-RSP message at the time where theperiodic ranging is completed, only when it detects the need to updatethe SLPID of the MS.

FIG. 3 is a flowchart illustrating an SLPID update process performed inan MS in a periodic ranging operation between a BS and the MS in thesleep mode in a communication system according to an embodiment of thepresent invention. Referring to FIG. 3, an MS stays in a sleep mode instep 301. That is, the MS stays in the state where it is allocated aninitial SLPID from the BS and transmits no data in the sleep mode. Instep 303, the MS determines if it is time to perform a periodic rangingprocess with the BS. If it is not time to perform the periodic rangingprocess, the MS continuously maintains the sleep mode. However, if it istime to perform the periodic ranging process, the MS transmits anRNG-REQ message to the BS for ranging request in step 305. Subsequently,in step 307, the MS receives an RNG-RSP message from the BS in responseto the ranging request.

In step 309, the MS determines if there is an SLPID_Update parameterincluded in the RNG-RSP message received from the BS to determinewhether its own SLPID is updated. If there is an SLPID_Update parameterincluded in the RNG-RSP message received from the BS, the MS updates itsown SLPID with the SLPID newly allocated by the BS according to theparameter information in step 311, and then returns to step 301,transitioning back to the sleep mode. However, if it is determined instep 309 that if there is no SLPID_Update parameter included in theRN-RSP message received from the BS, the MS maintains the old SLPIDcurrently allocated thereto and returns to step 301 to transition backto the sleep mode. The sleep mode in step 301 has a concept includingone or both the sleep interval or the listening interval.

Second Embodiment

The SLPID update method according to the second embodiment of thepresent invention is characterized by updating an SLPID using a TRF-INDmessage in a listening interval of the sleep mode. The SLPID updatemethod using the TRF-IND message according to the second embodiment ofthe present invention will now be described with reference to FIGS. 4,5A and 5B.

FIG. 4 is a flowchart illustrating a BS operation of updating an SLPIDof an MS through a TRF-IND message in a communication system accordingto an embodiment of the present invention. Referring to FIG. 4, at step401, a transmission time of a TRF-IND message occurs. In step 403, a BSdetermines if there is an MS requiring an SLPID update, for at least oneMS not required to transition to the awake mode among the MSs in thelistening interval of the sleep mode. That is, the BS determines ifthere is a need to update an SLPID for an MS that will continuouslymaintain the sleep mode. The process of determining if there is a needto update an SLPID is achieved by determining if there is any emptySLPID in a list of SLPIDs with a number less than that of the currentSLPID of the MS in the total SLPID list managed in the BS. The emptySLPID can correspond to an SLPID returned to the BS when another MSusing the SLPID previously allocated from the BS makes a mode change tothe awake mode. If there are a plurality of newly allocable emptySLPIDs, it is preferable to newly allocate and update the least SLPIDamong the empty SLPIDs. In this manner, an SLPID of the MS can becontinuously updated with a smaller SLPID rather than being fixed to theinitially allocated SLPID.

For example, assuming that the lowest SLPID that the BS can allocate tothe MS in the sleep mode is an SLPID#1 and an SLPID initially allocatedto the MS is an SLPID#99, if there are unused SLPIDs between the SLPID#1and the current SLPID#99 for the MS that has transmitted the RNG-REQmessage, the BS can newly allocate the least one of the empty SLPIDs tothe MS.

If it is determined in step 403 that there is an MS requiring SLPIDupdate, i.e., if the BS determines that there is an MS requiring SLPIDupdate while maintaining the sleep state for at least one MS in thelistening interval, the BS creates a TRF-IND message includinginformation on a new SLPID to be allocated to the MS requiring SLPIDupdate, i.e., information used for updating the SLPID of the MS in step405. More specifically, the BS creates the TRF-IND message by addinginformation on the SLPID currently used for the MS and information onthe SLPID to be newly allocated to the MS to an SLPID_Update field ofthe TRF-IND message.

In step 407, the BS creates an SLPID bitmap of the TRF-IND message bysetting a traffic indicator of the TRF-IND message for the MS requiringSLPID update to a negative indicator (bit=0) and setting an SLPID updateindicator to a positive indicator (bit=1).

If it is determined in step 403 that there is no MS requiring SLPIDupdate, in step 407, the BS creates the SLPID bitmap of the TRF-INDmessage by setting the traffic indicator to 0 (negative indicator) andthe SLPID update indicator to 0 (negative indicator) for the MS that hasno data traffic to transmit and does not require SLPID update. Althoughthe SLPID update is not required for the MSs, if there is data trafficto transmit, the BS creates the SLPID bitmap of the TRF-IND message bysetting the traffic indicator to 1 (positive indicator) for thecorresponding MS.

After creating the SLPID bitmap, the BS broadcasts the TRF-IND messageincluding the SLPID bitmap in step 409.

A format of the modified TRF-IND message broadcasted by the BS in step409 is shown below in Table 5.

TABLE 5 Syntax Size Notes MOB-TRF-IND_Message_Format( ){  ManagementMessage Type = 52  8 bits  FMT  1 bit 0 = SLPID based format 1 = CIDbased format  if(FMT==0){  Byte of SLPID bitmap  8 bits  SLPID bitmapVariable Two bits are allocated to one MS. 00: negative trafficindicator/negative SLPID update 01: negative traffic indicator/positiveSLPID update 10: positive traffic indicator 11: reserved } else { Num-pos  7 bits Number of CIDs on the positive indication list  for(i=0; i<Num-pos ; i++){   Short Basic CID 12 bit Basic CID  }  while(!byte_boundary){   Padding bits  1 bit padding for byte alignment  }  }}

As shown in Table 5, the SLPID bitmap information of the TRF-IND messageincludes bit information indicating the presence/absence of data trafficto be transmitted to the MS and bit information indicating whether toupdate the SLPID allocated to the MS. Of the two bits of the SLPIDbitmap, the first bit is a traffic indicator indicating thepresence/absence of traffic, and the second bit is an SLPID updateindicator indicating the presence/absence of SLPID update. For example,if SLPID bitmap information for the MS is ‘00’, it indicates that thereis no data traffic to be transmitted to the MS and there is no need toupdate an SLPID of the MS. If SLPID bitmap information for the MS is‘01’, it indicates that there is no data traffic to be transmitted tothe MS and there is a need to update an SLPID of the MS. Therefore, theMS must read SLPID_Update information included in TLV of the TEF-INDmessage and detect an SLPID newly allocated thereto. If SLPID bitmapinformation for the MS is ‘10’, it indicates that there is data trafficto be transmitted to the MS. Therefore, the MS indicates the necessityto make a mode change to the awake mode. In addition, because the SLPIDupdate process is not necessary for an MS having transmission datatraffic, if the first one bit of the SLPID bitmap is set to 1, the MSmust transition to the awake mode, regardless of a value of the last onebit.

Although the TRF-IND message according to the present invention hasshown and described with reference to an embodiment thereof, it is notlimited to the foregoing description. For example, according to anotherembodiment of the present invention, the TRF-IND message can be createdwith 1 bit. In this case, the TRF-IND message indicates only thepresence/absence of data traffic to be transmitted to the MS. If thereis no data traffic, the MS reads an SLPID_Update TLV included in thereceived TRF-IND message, and determines whether there is SLPIDinformation corresponding thereto, performing SLPID update.

When an SLPID update indicator of the TRF-IND message is set to apositive indicator, an SLPID_Update parameter is added to the TLVEncoding parameter of the TRF-IND message as is shown below in Table 6.

TABLE 6 Name Length Value SLPID_Update variable Compound Value NameLength (Variable length) For (i=0; i<N_SLPID_update; i++) {Old_New_SLPID 20 bits The first 10 bits indicate old SLPID and the last10 bits indicate new SLPID }

Referring to Table 6, the SLPID_Update parameter includes Old_New_SLPIDin which an OLD SLPID currently allocated to the MS and a NEW SLPID tobe newly allocated to the MS are stored in pair. Because the TRF-INDmessage including the SLPID_Update parameter is transmitted on abroadcast basis, the TRF-IND message can include as many SLPIDscurrently used by the MS and SLPIDs to be newly allocated to the MS asthe number of MSs requiring SLPID update.

FIGS. 5A and 5B are flowcharts illustrating an MS operation ofperforming SLPID update through a TRF-IND message in a communicationsystem according to an embodiment of the present invention. Morespecifically, FIG. 5A illustrates an exemplary MS operation for a 2-bitTRF-IND message, and FIG. 5B illustrates an exemplary MS operation for a1-bit TRF-IND message. That is, FIGS. 5A and 5B illustrate an SLPIDupdate operation of the MS in the case where an SLPID update indicatorof the MS in a TRF-IND message received in a listening interval of thesleep mode is set to 1 in a communication system according to anembodiment of the present invention.

Referring to FIG. 5A, an MS in the sleep mode currently stays in thelistening interval in step 501. For the listening interval, the MSreceives a TRF-IND message shown in Table 5 in step 503.

The MS, after receiving the TRF-IND message for the listening interval,analyzes information on an SLPID bitmap of the received TRF-IND message.That is, the MS checks the presence/absence of data traffic transmittedthereto and the necessity to update an old SLPID allocated thereto,based on the SLPID bitmap information of the received TRF-IND message.More specifically, the MS checks a bit value corresponding to a trafficindicator therefor in the SLPID bitmap of the TRF-IND message in step505.

If the traffic indicator value for the MS is set to 1, the MS enters theawake mode, recognizing the presence of data traffic to be transmittedthereto, and performs a traffic transmission/reception process with theBS in step 507. However, if the traffic indicator value is not set to 1,indicating the absence of data traffic to be transmitted to the MS, thenthe MS checks in step 509 if there is an SLPID to be newly allocatedthereto, by analyzing an SLPID update indicator value of the TRF-INDmessage.

If the SLPID update indicator value is set to 1, the MS reads anSLPID_Update TLV included in the TRF-IND message received in step 503,and acquires information on an SLPID newly allocated thereto in step511.

Because the SLPID_Update TLV occasionally includes SLPID information formore than one MS, the MS reads a value for the first 10 bits from anOld_New_SLPID of the SLPID_Update TLV to detect information beingcoincident with its current SLPID in step 511. As a result of thedetection, if the MS detects an Old_New_SLPID being coincident with itscurrent SLPID, the MS recognizes the last 10 bits of the Old_New_SLPIDas an SLPID newly allocated thereto. Subsequently, the MS updates itsown SLPID according to the SLPID allocated to the last 10 bits of theOld_New_SLPID.

In step 513, the MS enters the sleep mode after updating the SLPID.

If it is determined in step 509 that the SLPID update indicator value isnot set to 1, the MS maintains its current SLPID and stays in the sleepmode, in step 513, recognizing the non-necessity to update the SLPID.

Referring to FIG. 5B, an exemplary MS operation for a 1-bit TRF-INDmessage received from a BS, because steps 502 through 508 of FIG. 5B areequal to the steps 501 through 507 in operation, a detailed descriptionthereof will be omitted. However, FIG. 5B is different from FIG. 5A inthat the TRF-IND message received from the BS has a 1-bit value.Therefore, the process of FIG. 5B is the same as that of FIG. 5A exceptthat the TRF-IND message has a 1-bit value. As the received TRF-INDmessage has a 1-bit value, step 510 of FIG. 5B is different from step509 of FIG. 5A in operation.

That is, if it is determined in step 506 that the traffic indicatorvalue is not set to 1, indicating the absence of data traffic to betransmitted to the MS, the MS reads SLPID_Update information included ina TRF-IND message received from the BS in the form of TLV, anddetermines whether there is an SLPID newly allocated thereto, in step510. If there is an SLPID newly allocated thereto in the SLPID_UpdateTLV, the MS updates its SLPID with the new SLPID in step 512.

Because the SLPID_Update TLV occasionally includes SLPID information formore than one MS, the MS reads a value for the first 10 bits from theOld_New_SLPID of the SLPID_Update TLV, and detects information matchingits current SLPID. If the MS detects an Old_New_SLPID corresponding toits current SLPID, the MS updates the SLPID newly allocated thereto withthe last 10 bits of the Old_New_SLPID, and then enters the sleep mode,in step 514. Upon failure to detect SLPID information corresponding tothe MS, the MS remains in the sleep mode in step 514, therebymaintaining its current SLPID.

Third Embodiment

The SLPID update method according to the third embodiment of the presentinvention is characterized by updating an SLPID using an unsolicitedSLP-RSP message in a listening interval of a sleep mode. With referenceto FIGS. 6 and 7, a description will now be made of an SLPID updatemethod using an unsolicited SLP-RSP message according to the thirdembodiment of the present invention.

FIG. 6 is a flowchart illustrating a BS operation of updating an SLPIDof an MS using an unsolicited SLP-RSP message in a listening interval ofa sleep mode in a communication system according to the third embodimentof the present invention. Referring to FIG. 6, a BS determines in step601 whether there is a need for SLPID update for MSs staying in thelistening interval of the sleep mode. It is assumed herein that theleast SLPID number that the BS can allocate to an MS staying in alistening interval of the sleep mode is an SLPID#1. In this case, theprocess of determining in step 601 whether there is a need for SLPIDupdate for MSs staying in the listening interval of the sleep mode isachieved in the following manner. The BS determines whether there is anyunallocated SLPID, i.e., any empty SLPID, between an SLPID currentlyallocated to the MS in the listening interval of the sleep mode and theSLPID#1, and if there is an empty SLPID, the BS determines that there isa need to update an SLPID of the MS.

If it is determined in step 601 that there is a need for SLPID updatefor a particular MS, the BS determines, as an SLPID to be newlyallocated to the MS, an SLPID with the least number among the unusedempty SLPIDs between the SLPID allocated to the MS and the least SLPIDallocable by the BS. In step 603, the BS sets a Sleep-Approved value inthe SLP-RSP message to 1, defines interval information of the SLP-RSPmessage, i.e., Start Frame value, Initial-Sleep Window value,Final-Sleep Window value, and Listening Interval information, asinterval information currently used by the MS, and stores the intervalinformation together with the newly determined SLPID information in theSLP-RSP message.

In step 605, the BS transmits an SLP-RSP message including the SLPIDnewly allocated to the MS and the interval information, to thecorresponding MS.

FIG. 7 is a flowchart illustrating an MS operation of performing SLPIDupdate using an unsolicited SLP-RSP message in a listening interval ofthe sleep mode in a communication system according to an embodiment ofthe present invention. Referring to FIG. 7, an MS stays in a listeninginterval of the sleep mode in step 701, and receives an SLP-RSP messagefrom a BS in step 703. Upon receiving the SLP-RSP message from the BS,the MS analyzes an SLPID included in the SLP-RSP message. If the MSdetects the necessity to update the SLPID allocated thereto through theSLP-RSP message, the MS updates its own SLPID with the SLPID in theSLP-RSP message in step 705. The other interval information except forthe SLPID is disregarded.

The SLP-RSP message used for instructing SLPID update as illustrated inFIGS. 6 and 7 includes the interval information for the sleep modeoperation of the MS in addition to the SLPID information. The intervalinformation is unnecessary for an MS in the sleep mode. Therefore, thepresent invention proposes a format of a new SLP-RSP message notincluding the unnecessary interval information. A format of the modifiedSLP-RSP message according to an embodiment of the present invention isshown below in Table 7.

TABLE 7 Syntax Size Notes MOB-SLP-RSP_Message_Format( ){  Managementmessage type = 51  8 bits  Sleep-approved  1 bit 0: Sleep-mode requestdenied 1: Sleep-mode request approved  if(Sleep-approved==0) { After-REQ-action  1 bit 0: The MS may retransmit the MOB- SLP-REQmessage after the time duration (REQ-duration) given by the BS in thismessage. 1: The MS shall not retransmit the MOB-SLP-REQ message andshall await the MOB-SLP-RSP message from the BS  REQ-duration  4 bitsTime duration for case where After- REQ-action value is 0.  reserved  2bits  }  else {  SLPID_Update  1 bit 0: BS provides the information forsleep mode operation 1: BS informs Sleep ID update  if(SLPID_Update==0){  Start frame  6 bits   initial-sleep window  6 bits   final-sleepwindow base 10 bits   listening interval  4 bits   final-sleep windowexponent  3 bits   SLPID 10 bits   reserved  7 bits  }  else{   SLPID 10bits   reserved  4 bits  }  } }

As shown in Table 7, the proposed SLP-RSP message includes anSLPID_Update field used for determining whether the SLP-RSP message is amessage transmitted for an SLPID update operation or a messagetransmitted to indicate SLPID and interval information to be used in thesleep mode operation performed when starting the existing sleep modeoperation. For a SLP-RSP message transmitted to start the sleep modeoperation of the MS, the BS sets the SLPID_Update field value to 0, andstores start time of the sleep mode operation, initial-window size,final-window size, listening interval, and SLPID information. When thereis a need to update an SLPID of the MS during a sleep mode operationwith the MS, i.e., when the SLP-RSP message is a message transmitted toinform the MS of a new SLPID, the BS sets the SLPID_Update field valueto 1 and stores information on only an SLPID to be newly allocated.

The SLP-RSP message shown in Table 7 can be created such that itincludes interval information necessary for the sleep mode operation inaddition to the SLPID in the form of TLV of the SLP-RSP message. In thiscase, when the MS and the BS perform a sleep mode entry negotiationprocess using the modified SLP-RSP message, the SLP-RSP message can becreated such that it includes Interval_Info TLV, i.e., start time of thesleep mode operation, initial-window size, final-window size, andlistening interval.

Therefore, when the SLP-RSP message is use used to give instructions toupdate an SLPID of the MS, the BS performs an SLPID update operation bytransmitting the SLP-RSP message without the interval information suchas the Interval_Info TLV to the MS. When the SLP-RSP message is used togive instructions to perform a sleep mode operation, the BS transmitsthe SLP-RSP message with the interval information such as theInterval_Info TLV to the MS.

Fourth Embodiment

FIG. 8 is a flowchart illustrating a BS operation for updating an SLPIDof an MS using a modified SLP-RSP message in a listening interval of asleep mode in a communication system according to another embodiment ofthe present invention. Referring to FIG. 8, if it is time to transmit aTRF-IND message (step 801), a BS selects an MS not requiring to enterthe awake mode among the MSs in the listening interval of the sleepmode, i.e., selects an MS not requiring to perform SLPID update amongthe MSs having no traffic to transmit, in step 803. The process ofdetermining the necessity to update the SLPID has been described above.

Next, the BS must enable the MS in the sleep mode to transition to theawake mode in order to send a SLP-RSP message for SLPID update to theMS. Therefore, the BS sets a traffic indicator corresponding to the MSin the SLPID bitmap of the TRF-IND message to 1 in step 805. Thereafter,in step 807, the BS sets a Sleep-Approved field value of the SLP-RSPmessage to 1 in order to inform the MS of the SLPID update, andtransmits the SLP-RSP message with the newly allocated SLPID informationstored therein, to the MS.

FIG. 9 is a flowchart illustrating an MS operation of performing SLPIDupdate by receiving a modified SLP-RSP message in a listening intervalof the sleep mode in a communication system according to an embodimentof the present invention. Referring to FIG. 9, an MS staying in alistening interval of the sleep mode (step 901) receives a TRF-INDmessage from a BS in step 903. In step 905, the MS checks the TRF-INDmessage received from the BS to determine if its own traffic indicatoris set to 1. If its traffic indicator is not set to 1, i.e., is set to anegative indicator, the MS enters the sleep mode, recognizing theabsence of data traffic to be transmitted thereto, in step 917. However,if its traffic indicator in the TRF-IND message is set to 1, i.e., isset to a positive indicator, the MS transitions to the awake mode totemporarily wake up from the sleep mode, recognizing the presence ofdata traffic to be transmitted thereto, in step 907.

Upon receiving an SLP-RSP message from the BS in the awake mode in step909, the MS checks a bit value of an SLPID_Update field of the SLP-RSPmessage in step 911. If no SLP-RSP message is received from the BS inthe awake mode, the MS waits for the reception of transmission datatraffic in the awake mode.

If the SLPID_Update field is set to 1, the MS updates its current SLPIDwith a new SLPID included in the SLP-RSP message in step 915,recognizing the necessity to update its own SLPID. Subsequently, in step917, the MS enters the sleep mode after the SLPID update.

However, if it is determined in step 911 that the SLPID_Update field isnot set to 1, the MS acquires interval information necessary for thesleep mode operation and information on an SLPID allocated thereto instep 913, recognizing a new start of the sleep mode operation.Thereafter, in step 917, the MS enters the sleep mode.

As described above, the novel BWA communication system can update anSLPID allocated to an MS in a sleep mode. As the communication systemsupporting the sleep mode can update an SLPID allocated to the MS in thesleep mode, it can reduce a size of an SLPID bitmap, contributing to areduction in the processing time required for reading and processing theSLPID bitmap. That is, the communication system enables an SLPIDallocated to the MS in the sleep mode to be updated even in the sleepmode rather than being fixed, reducing the number of SLPID bitmaps to beprocessed by the MS in the sleep mode state. As a result, the novelprocess of processing a TRF-IND message by the MS in the sleep mode ismore effective than the conventional process.

While the present invention has been shown and described with referenceto certain exemplary embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the presentinvention as defined by the appended claims.

1. A method for updating a sleep identifier (SLPID) by a base station(BS) in a broadband wireless access (BWA) communication system, themethod comprising: transmitting a message including SLPID updateinformation to a mobile station (MS) in sleep mode operation when thereis no traffic directed to the MS, wherein the SLPID update informationincludes information on an old SLPID allocated to the MS and a new SLPIDallocated to the MS for updating the old SLPID, and an SLPID is uniquelyassigned by the BS whenever an MS is instructed to enter a sleep mode,wherein the SLPID update information includes M bits, the first M/2 bitsamong M bits indicate the old SLPID, the last M/2 bits among M bitsindicate the new SLPID, and M is an integer greater than 2, and whereinthe message is a traffic indication (MOB_TRF-IND) message, and theMOB_TRF-IND message includes a negative indication when there is notraffic directed to the MS.
 2. The method of claim 1, wherein the newSLPID is one of other SLPIDs different from the old SLPID, the otherSLPIDs are empty SLPIDs, each of the empty SLPIDs is an SLPID, returnedto the BS, which was previously allocated to other MS.
 3. A system forupdating a sleep identifier (SLPID) in a broadband wireless access (BWA)communication system, the system comprising: a mobile station (MS) insleep mode operation; and a base station (BS) for transmitting a messageincluding SLPID update information to the MS when there is no trafficdirected to the MS, wherein the SLPID update information includesinformation on an old SLPID allocated to the MS and a new SLPIDallocated to the MS for updating the old SLPID, and an SLPID is uniquelyassigned by the BS whenever an MS is instructed to enter a sleep modeswherein the SLPID update information includes M bits, the first M/2 bitsamong M bits indicate the old SLPID, the last M/2 bits among M bitsindicate the new SLPID, and M is an integer greater than 2, and whereinthe message is a traffic indication (MOB_TRF-IND) message, and theMOB_TRF-IND message includes a negative indication when there is notraffic directed to the MS.
 4. The system of claim 3, wherein the newSLPID is one of other SLPIDs different from the old SLPID, the otherSLPIDs are empty SLPIDs, each of the empty SLPIDs is an SLPID, returnedto the BS, which was previously allocated to other MS.
 5. A method forupdating a sleep identifier (SLPID), by a mobile station (MS) in sleepmode operation, in a broadband wireless access (BWA) communicationsystem, the method comprising: receiving, from a base station (BS), amessage including SLPID update information including information on anold SLPID allocated to the MS and a new SLPID allocated to the MS forupdating the old SLPID; and updating the old SLPID to the new SLPID,wherein the message is transmitted when there is no traffic directed tothe MS, and an SLPID is uniquely assigned by the BS whenever an MS isinstructed to enter a sleep mode, wherein the SLPID update informationincludes M bits, the first M/2 bits among M bits indicate the old SLPID,the last M/2 bits among M bits indicate the new SLPID, and M is aninteger greater than 2, and wherein the message is a traffic indication(MOB_TRF-IND) message, and the MOB_TRF-IND message includes a negativeindication when there is no traffic directed to the MS.
 6. The method ofclaim 5, wherein the new SLPID is one of other SLPIDs different from theold SLPID, the other SLPIDs are empty SLPIDs, each of the empty SLPIDsis an SLPID, returned to the BS, which was previously allocated to otherMS.
 7. A system for updating a sleep identifier (SLPID) in a broadbandwireless access (BWA) communication system, the system comprising: abase station (BS); and a mobile station (MS) for receiving, from the BS,a message including SLPID update information including information on anold SLPID allocated to the MS and a new SLPID allocated to the MS forupdating the old SLPID, and updating the old SLPID to the new SLPID,wherein the MS is in sleep mode operation, the message is transmittedwhen there is no traffic directed to the MS, and an SLPID is uniquelyassigned by the BS whenever an MS is instructed to enter a sleep mode,wherein the SLPID update information includes M bits, the first M/2 bitsamong M bits indicate the old SLPID, the last M/2 bits among M bitsindicate the new SLPID, and M is an integer greater than 2, and whereinthe message is a traffic indication (MOB_TRF-IND) message, and theMOB_TRF-IND message includes a negative indication when there is notraffic directed to the MS.
 8. The system of claim 7, wherein the newSLPID is one of other SLPIDs different from the old SLPID, the otherSLPIDs are empty SLPIDs, each of the empty SLPIDs is an SLPID, returnedto the BS, which was previously allocated to other MS.